Measurement of heat content of combustible fuel mixtures



United States Patent ABSTRACT OF THE DISCLOSURE A bomb calorimeter formeasuring heat of combustion includes electrical means for measuringheat required to ignite the fuel and means for subtracting the heatproduced by energizing the firing wire from the total measured heat.

This invention is related generally to the measurement of the heatliberated during combustion of a combustible fiuid, and moreparticularly to a bomb calorimeter and apparatus associated therewithfor making extremely accurate heat measurements by measuring the heatadded to to the system by ignition of the firing means thereof.

Bomb calorimeters have been used for many years for the purpose ofmaking accurate heat measurements. In j the past few years various fuelshave been developed for applications in which it is important to knowthe energy content of the particular fuels to an extremely high degreeof accuracy. It is desirable to use bomb calorimeters for suchapplications because of the convenience and the ease of operationthereof.

It has now been discovered that a major cause of error in bombcalorimeters is the variable amount of heat liberated by the firingmeans thereof during a heat measurement. The most desirable type of bombcalorimeter for use in highly accurate heat measurements is a type making use of a low resistance firing wire that fuses during the ignitionof the explosive fluid mixture which is undergoing an energy contentdetermination.

In accordance with one aspect of the invention, there is connectedbetween the firing means of a bomb calorimeter and an electricalterminal means to which connection to an electrical source may be made,a circuit means for measuring the electrical power consumed by thefiring means when the firing means is electrically energized.Preferably, the circuit means includes a multiplying circuit means forconnecting the firing means to the terminal means adapted to produce anoutput voltage proportional to the power consumed by the firing means,along with integrating means for producing an output indication of thetime integral of the output power of the electrical circuit means. Inaddition, means is provided electrically connected to the firing meansfor detecting the fusing of the firing means and for disconnecting theintegrating means from the electrical circuit means upon said detection,which it has been found will produce an exceedingly accurate powermeasurement.

Objects and features of the invention which are not apparent from theabove discussion will become evident upon consideration of the followingdetailed description of the invention when taken in connection mm theaccompanying drawing, wherein the single figure illustrates a preferredembodiment of the invention in the form of an electrical schematicdiagram, partially in block form.

With reference now to the figure, there is shown a bomb calorimeter 1 inblock form, which bomb calorimeter is of the type having a lowresistance wire firing device 3 which, when electrically energized, willproduce heat sufliciently high to ignite a fluid combustible mixture inthe bomb calorimeter. The firing wire 3 may be an element of nichrome orother alloys of about 5 3,368,401 Patented Feb. 13, 1968 ohmsresistance. The wire may be 1 to 4 inches in length.

There is also provided a plurality of terminals 73, 75, and 79 forconnection to a three-wire alternating current source, which may be a110 volt A.C. single phase source. Terminal is grounded, and terminals73 and 79 are connected to the primary 57 of power transformer 59through contact 67 of push-button switch 69. Power from the alternatingcurrent souce is supplied to firing device 3 from the secondary winding55 of transformer 59 through the electrical circuit described below.

Reference numeral 5 designates a multiplying device adapted to producean output voltage at terminals 15, 17 proportional to the product of thecurrent flowing therethrough (applied to terminals 7, 9) and the voltageapplied thereto (applied to terminals 11, 13). The function ofmultiplying device 5 is to, in effect, measure the power consumed byfiring means 3 responsive to a voltage applied thereto. Thus, firingmeans 3 is connected in series circuit relationship with terminals 7, 9,current limiting resistor 53, and the secondary winding 55 of powertransformer 59. The voltage input terminals 11, 13 of multiplying device5 are connected respectively to one side of firing device 3 and toterminal 9 through resistor 19. The multiplying device 5 may be of thetype manufactured by Bell, Inc. of Columbus, Ohio, Model No. HM3011.

The output voltage of multiplying circuit 5 is integrated by anintegrating amplifier including an integrating capacitor 63. The inputcircuit of the integrating amplifier 61 is connected to output terminals15, 17 of multiplying device 5 through a normally closed contact 43 ofrelay 45, and a series resistor 21. A resistor 23 is connected inparallel across the lines between the output terminals 15, 17 and theinput circuit of amplifier 61. The function of resistors 21, 23 is toestablish specified load to multiplier such that this device will meetspecified output, linearity, and temperature compensation. The outputsignal of integrating circuit 61 is measured by a voltmeter 71 which maybe a Weston Model 911 DC. voltmeter having a sensitivity of 20,000 ohmsper volt.

The function of relay 45 is to remove the output signal ofcross-multiplying circuit 5 from the input circuit of integratingamplifier 61 at the instant that firing device 3 fuses. Power forenergizing the control winding of relay 45 is derived through powertransformer 51 from terminals 73, 79. The secondary winding 47 oftransformer 51 is connected to the relay actuating winding 45a betweenelectrodes 41 and 37, the control rectifier will conduct to energize theactuating winding 45a and open contact 43. The actuating signal foractuating the control rectifier 35 is derived from a bridge rectifierwhich is in electrical circuit relationship with the firing means 3.More specifically, the input terminals of the bridge rectifier areconnected between firing means 3 and resistor 53 so that when the firingmeans 3 fuses, the voltage drop across resistor 53 will substantiallydisappear, and the voltage applied to input terminals of the bridgerectifier 25 will rise to substantially the voltage across secondarywinding 55 of transformer 59. The output terminals of bridge rectifier25 are coupled between rectifier electrodes 37, 41 through a rheostat orpotentiometer 27 having a variable tap 29 connected across the bridgerectifier output terminals, and a series resistor 31 connected betweentap 29 and electrode 41. Resistor 33 is connected between electrodes 41and 37 in the usual manner. Electrode 37 is connected to the negativeone of the output terminals of bridge rectifier 25.

Push-button switch 69 is provided with a second contact 65 which isconnected across the integrating capacitor 63 of integrating amplifier61. Contact 65 is normally closed, and contact 67 is normally open sothat when the contact 67 is closed to energize the primary winding 57 oftransformer 59, and thereby energizing the firing means 3, theshort-circuit across capacitor 63 is simultaneously removed.

The operation of the apparatus described above is as follows. The bombcalorimeter is initially charged with a combustible fuel and firingmeans 3 is checked to see that it has not been previously fused. Anappropriate A.C. source is connected to terminals 73, 75, and 79. Whenpush-button 69 is actuated to close contact 67 and open contact 65, thefiring means 3 will be energized and the voltage applied to bridgerectifier 25 will be sufficiently low as not to activate controlrectifier 35 so that contact 43 will remain closed. The output voltageappearing across terminals 15, '17 will be proportional to the currentand voltage applied to resistive firing means 3 until the firing meansfuses. At this instant, the voltage applied to bridge rectifier 25 willrise to activate the control rectifier 35 and pick up the relay 45 sothat any stray output voltage from multiplying circuit 5 will be removedfrom the input of integrating circuit 61. Thus, the voltage output ofthe integrating circuit will be proportional to the energy consumed bythe firing means 3 during the interval between the instant at whichconstant 67 was closed and the instant at which the firing means 3fused. This output voltage can readily be converted to heat units, suchas B.t.u.s from the formula where E is the voltage of meter 71, K is acalibration constant, and B.t.u.s is the measured heat.

This heat quantity will be subtracted from the heat of combustion of theexposive mixture in the horn calorimeter measured by the bombcalorimeter.

The leads between terminals 15, 17 and the input of the integratingcircuit 61 should be shielded as much as possible, as illustrated, sothat there will be no stray voltages picked up thereby which can beintegrated by the integrating circuit during a measurement.

The invention is not necessarily to be restricted to the specificstructural details, arrangement of parts, or circuit connections hereinset forth, as various modifications thereof may be effected withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustiblefuel, said calorimeter including a firing means for igniting thecombustible fluid in said calorimeter when said firing means selectrically energized;

electrical terminal means for connection to an electrical energy source;and

circuit means connecting said terminal means to said firing means formeasuring the electrical power consumed by said firing means when saidfiring means is electrically energized; said circuit means includingmultiplying means adapted to produce an output voltage proportional tothe power consumed by the firing means, integrating means adapted toproduce an output indication of the time integral of said output power,and means for detecting the heat produced by energization of said firingmeans and for disconnection of said integrating means on detection ofsaid heat.

2. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustiblefluid, said calorimeter including a fusible firing means for ignitingthe combustible fluid in said calorimeter when said firing means iselectrically energized;

electrical terminal means for connection to an electrical energy source;and

circuit means selectively connecting said terminal means to said firingmeans, including means for measuring the total electrical energyconsumed by said firing means from the instant that said firing means iselectrically energized and until the instant of fusing thereof; saidcircuit means including multiplying means adapted to produce an outputvoltage proportional to the power consumed by the firing means,integrating means for producing an output indication of the timeintegral of the output of said circuit means, and means for detectingthe fusing of the firing means and for disconnection of the integratingmeans on detection of said fusion.

3. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustiblefluid, said calorimeter including a fusible firing means for ignitingthe combustible fluid in said calorimeter when said firing means iselectrically energized;

electrical terminal means for connection to an electrical energy source;

electrical circuit means connecting said firing means to said terminalmeans for producing an output voltage proportional to the power consumedby said firing means;

integrating circuit means for producing an output indication of the timeintegral of said output power of said electrical circuit means; and

means electrically connected to said firing means for detecting thefusing of said firing means, and for disconnecting said integratingmeans from said electrical circuit means upon said detection.

4. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustiblefluid, said calorimeter including a fusible firing means for ignitingthe combustible fluid in said calorimeter when said firing means iselectrically energized;

electrical terminal means for connection to an electrical energy source;

circuit means selectively connecting said terminal means to said firingmeans, including means for measuring power consumed by said firing meansafter said firing means is electrically energized and prior to fusingthereof;

said circuit means including multiplying circuit means for producing anoutput voltage proportional to the product of voltage applied to saidfiring means and current consumed by said firing means;

a voltage integrating circuit;

a relay having contact means normally connecting said integratingcircuit means to said multiplying circuit means whereby said integratingcircuit will integrate the multiplying circuit output voltage, and anactuating winding for opening said contact when energized;

means including electrical valve means having a control electrode,connecting said actuating winding to said electrical terminal means, forenergizing said actuating winding responsive to a predetermined controlsignal applied to said control electrode; and

control circuit means electrically connected to said control electrodeand to said firing means, for detecting the fusing of said firing meansand thereupon applying said predetermined control signal to said controlelectrode.

5. The combination of claim 4 wherein said control circuit meansincludes resistor means connected in series circuit relationship withsaid firing means, and rectifier means having input terminals connectedbetween said resistor and said firing means, and having an outputcircuit electrically connected to said control electrode, whereby theoutput voltage thereof applied to said control electrode will increasewhen said firing means fuses.

6. In combination:

a bomb calorimeter for measuring the heat of combustion of a combustiblefluid, said calorimeter including a fusible firing means for ignitingthe combustible fluid in said calorimeter when said firing means iselectrically energized;

electrical terminal means for connection to an electrical energy source;

circuit means selectively connecting said terminal means to said firingmeans, including means for measuring power consumed by said firing meansafter said firing means is electrically energized and prior to fusingthereof;

said circuit means including multiplying circuit means for producing anoutput voltage proportional to the product of voltage applied to saidfiring means and current consumed by said firing means;

a voltage integrating circuit including an integrating capacitor;

a relay having contact means normally connecting said integratingcircuit to said multiplying circuit means whereby said integratingcircuit will integrate the multiplying circuit output voltage, and anactuating Winding for opening said contact means when energized;

means including electrical valve means having a control electrodeconnecting said actuating winding to said electrical terminal means, forenergizing said actuating winding responsive to a predetermined controlsignal applied to said control electrode;

control circuit means electrically connected to said control electrodeand to said firing means, for detecting fusing of said firing means andthereupon applying said predetermined control signal to said controlelectrode, said control circuit means including resistor means connectedin series circuit relationship with said firing means, and rectifiermeans having input terminals connected between said resistor and saidfiring means, and having an output circuit electrically connected tosaid control electrode, whereby the output voltage thereof applied tosaid control electrode will increase when said firing means fuses; andcontrol switch means having first contact means connected to saidintegrating capacitor, and second contact means connected between saidterminal means and said resistor means, for short-circuiting saidcapacitor when said firing means is not electrically energized, and forsimultaneously removing said short circuit and electrically energizingsaid firing means.

References Cited UNITED STATES PATENTS 1,163,367 12/1915 Riche 73-191OTHER REFERENCES Jessup, R. S.: Brecise Measurement of Heat ofCombustion With a Bomb Calorimeter. In U.S. National Bureau of StandardsJournal of Research Monograph No. 7, page 9.

JAMES J. GILL, Primary Examiner.

E. E. SCOTT, Assistant Examiner.

